Telephone-exchange system.



A. E. LUNDELL.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JAN. II, 1916.

Patented July 2, 1918.

//7 Men for:

W M u L W m ALBEN n. LUNIDELL, or NEW YORK, N. Y.,

' moORroRATnn, on NEW YORK,

ASSlIGNOR To wEsTnRN ELECTRIC COMPANY, n. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

' Patented July 2, 1918.

Application filed January 11,1916. Serial No. 71,540.

To all whom it may concern:

Be it known that I, ALBEN E. LUNDELL, a citizen of the United States, residing at New York, in the county of Bronx and State of New York, have invented certain new and useful Improvements in Telephone-EX- change Systems, of which the following is a full, clear, conclse, and exact description.

This invention relates to telephone systems, and more particularly to improve ments in busy test circuits as employed on telephone switchboards. I

The principal object of this inventionis to provlde means whereby a busy test indication will be efi'ective only with the receiver of an operators telephone set; and not eifectivewith a telephone circuit connected in proper talking relation with the operators set. Another object of this invention is the provision of a telephone system wherein one party may ascertain whether the telephone of a second party is in use or not without giving any indication thereof to a third party, whose telephone is in talking relationship with the telephone of thelfirst party. 7

In accordance with one embodiment of this invention, a trunk circuit operators telephone set is equipped with a plurality of current transformers of an inductive type. The current encountered when a busytest operation is applied to a subscribers line circuit'on which a connection is present acts on one of transformers to induce a current in the telephone receiver of the operator applyingthe test. The same current also acts on another one ofthe transformers to neutralize the induced busy test currents with respect to that portion of the operators set to which an exterior telephone circuit is adapted'to be connected.

More specifically, this invention embodies separated switchboards or telephone central oflices-betweenwhih connections are completed by ,means'of trunk'circuitSQ Ata trunk. operators position each trunk circuit terminates in a cord and plug, and is provided withoalistening key, anda "signal adapted to beoperated-when a'call originates at theisending iendof a trunk circuit.

A call is answered by meansofthe listening key associated withfthe trunk on .whicha call ispresent, "and on an. order being receivedthereover, the trunk circuit operator tests the line circuit of the sub criber wanted in a multiple ,ing the features ofthis invention.

circuit 1. By means of an Operators teleby touching the tip of the trunk plug to the shell of the subscribers linejack which is a well-known operation. During the time the operator is applying this busy test, the l stening key may remaln in the talking po-- s1t1on with respect to the operators set and the trunk circuit, and this invention .provides. that in case a busy condition is encountered on the line tested, the characteristlc busy signal indication will only be manifested in the operatorstelephone' receiver and not 'on the trunk circuit.

p This invention is illustrated diagrammatically in the accompanying drawing, in which is shOWn' only such portions of a telephone exchange equipment as will be necessary in describing the features of this busy test system. The reference numeral 1 indicates a subscribers line circuit terminating type central energy switchboard, and another similarly equipped subscribers line terminating in another switchboard is indicated at 2. At thefirst switchboard a link circuit 3 is employed for completing telephone connections, and a trunk circuit 4 extends from the first to the second switchboard. An operators telephone set 5 at the receiving end of the trunk circuit 4 is equipped in a manner suitable for practis- Referring to the drawing, the operation of this system willbe apparent froma description of the steps. necessary in the handling of a call originating at the station 1 in which it is desired to secure ac onnection,

with the station 2.

This call is first manifested on a line signal 6, whereuponan operator inserts a plug 7 of the link circuit 3 into a jack 8 of the line phone set (not shown) the operator talks "with the calling party at the station 1, and on receiving a request for connection'with the subscriber2inserts a plugQOfthelink circuit 3 into a jack 10 of the trunk circuit 4. I

.yBatter'y current toth'e link circuit 3 operates a relay :11 at the distant end of the trunk circuit, thereby In response to this signahanoperator at 5 setsa listening key 13 and talks either with the originating operator at 3 or with the lighting a signal'lamp 12.

subscriberat station 1' (it will be understood that a transmitter, not shown-,isassociated with the operators telephone set at 5), and in we r rs c eese with the station 2. In order to determine the idle or busy condition of the line 2, the trunk operator momentarily-touches the tip of a trunk plug 14 to' the sli'e'll of ajack 15 01:

5 the line 2, and if no click is heandin, atelephone receiver 31, the plug'l l is inserted in this jack. T he relay .17 now operates oyer the'signal circuit conductors of this connection in series with the cuteoif; relay'18of'; the line circuit 2. contact member '19 of the ;rela-y 17 disconnects the path :to earth ouer ;which the; elamprl2 was first lighted, and conmects, a; re istance unit; 20 to complete. :a -cir- ,euitthrough the contactsof the: relay 11,

whereby the; lamp 12; is; shuntedand iaccoit ingly-extinguished. A contact niember '20' of the relay 17 disconnects the tip conductor of thegtrunk circuit, plug 14L from, thei-priinary windi-ngs 2;8vand= 24 of two transform- 20 ers, 21512111111 22, respectiyelyzandcompletes the continuity vof: the; tip; conductor, o f. the; trunk circuit 4 Although not showlnaitiwillzbe iuiderstoodi thata suitable source of ringing current is; present with? the: link-circuit 1 portion-of thetrunk lfor operating 1a call. signaliat thestation '2.

'Letlit now be assumed: that the call just considered, instead of: finding theline 2 idle, meets a busy condition of this 1 line circuit.

A busy condition of: the line 2 may,i f.orxconit venience, be. considered as present on the insertion of ,a;plug 129: in a .jack .30, which is common to-this line. Although complete circuits arenotzshownzfor the plugv29, it will ibe'understood that these circuits may be consideredias extending to airtrunk circuitlsimiilar to A 'ora link circuit similar; toa3, suitable for completing a i telephone. connection be tween "two subscribers lines. Under this condition, when the call from station 1 .reaohesthe operator ,at 5, and this. operator touches the tip, of theeplu'gz 14:.to; the shell.- of

the jack :15 in 1 making the necessary ibusy test; ofithe'lline 2, currentifrom a grounded :battery connected to: theQsignal circuit. conductor of the plug 29 Will flowiover'the 'tip circuit of the;'plug:14.-, thenormalcontact of '2 the member. of; relay; 17 and the: primary :W-iIldi-ngs 23 and 2 L of they transformers :21 and 22;-respect-ively,1 to earth. Although; this impulse ofebusy; test current through the. pri- ,mary windings-23 and24l-of the transformers induces, a corresponding impulselof; current ii-n leach of i, the I secondary windings .25 and 26 of; the, transformers, .the latter windings eare connected in series insuch-qrelation one :Witll the; other that the current polarityzsign induced inoneecoil presents anopposing cur- :rent polarity :sign 5 to the current; induced in the other coil. iThe two transformers are exactlyvbalancedasttoxcurrent-- reproduction;

itherefore the sinductive effect of :the transaforniers neutralize with respect to ;th'e serially connected windings'25 and- 26; which .1165 aare in turniincluded:bysmeansof the listening key 13 in bridge on the main conductors of the trunk circuitt. Accordingly induced current impulses through "the windings and-26 of "the transformers 21 and22 respectively, vdo,notuproduce current action in the main conductors of the trunk circuit.

T he manner in which busy testjmpulses are manifested in the operators telephone ;-receiYera3lcmaythe. described as follows: It

will be noted that the telephone receiver 31 is connected in sser-ies with a. condenser-2.8 sand 1' that this -.ser.ies circuit -.is included in bridge :on. the secondary winding 26 of: the

transformer 22 therefore the receiverviil 1s amcluded 11bit. closed clrcuit formed; through i 8 0 thetranstormer winding '26 independently of the secondary wuiidin'g225 of theuother transformer 21. I Currents induced .the minding 24. in the-secondary winding 26 of thetransformer 22, circulate: freely: thrcugh 8 5 the telephonevreceiverBi -which actionta-kes place when busy test current 1s encountered onxasubscribers line circuit as :described.

'A resistance .unit27 connected in bridge on -thesecondary Wllid-lngQli of the transformer 21, .serves: toaeliminate L the effective or imrpedancere sistance effect of; the winding.- 25 incompleting a series circuit, whereby the telephone receiver?) 1] is included by. means of theilistening key 'i1:3.i n bridge on c-the1inain conductors of the trunk circuit 4 for thepurpose 00f ihol'ding \telephone a communication thereover. ilhe resistance unit. 27; alsolserves :to maintain asymmetrical current condition with-respect to=the secondary windings 2 5 and 26 of the transformers 21 and 22, by con- ;suming anamount of current induced in: the coil '25 approximately .cqualzto .r the current consumediby the circuit of -the1receiver.31, -W-hich current is? that inducedrinithe COili'Qii. 1 5

From theforegoing description "it will be apparentthat although currents indueediby a busy test op eration may :be 2 heard A in the 1 telephone a receiver 31 during the ttime this receiver is connected to thezmainconductors of: the. trunk circuit 4,= no! current eifectLfr m such -busy :test indication will'lhowever, ibe :present on: thetrunk circuit.

It} will be understood that thes-ubscribers :line 1 mayiterminateiin an automatic ex- 116 change, in which :oasey .suitable tgselector j switch equipment iwould belemployed connectingithesubscribers lined" with the trunk circuita l, andaccordin-gly the manually operated links-circuit 3and 'the' j-acks associatejd .12 .with: the line circuit l an'd'i the trunk circuit 4 dispensed-with. 1

"iT he relays and signal lamps associated I with the" link ei-rcuit' are of a well know-n supervisory typeand-therefore-donotrequire 5 to beifurtherdescribed. A- 'supervisory relay :32 on the trunk circuits talso 1 operates -a -well+known way, -an'd the lamp 12; in addi- :tion' 5 to acting as a call signal also serves as a 1 disconnect 11 "signal on a I connected trunk. 1-30 fective with respect to the line with which said telephone receiver may be connected.

2. In a telephone exchange system, a telephone line, an operators telephone circuit including a receiver, switching means for including said operators receiver in circuit with said line, a busy test circuit, and current transforming means for rendering the current through said busy test circuit effective with respect to the operators receiver and neutralizing the current with respect to the line with which said receiver may be connected.

3. In a telephone exchange system, a subscribers line, an operators circuit including a receiver, switching means for connecting said receiver with said telephone line, a busy test circuit including a source of energy, current transforming means in said busy test circuit for inducing a current in said telephone receiver, and a second current transr forming means in said busy test circuit for producing a current flow equal to that through said first transforming means but in the opposite direction, said second transforming means being connected in the circuit 4:. In a telephone exchange system, a subscribers line, an operators circuit including a receiver, switching means for connecting said receiver with said subscribersline,

a busy test circuit, a current transforming 7 means having its primary 111 said busy test circuit and its secondary in multiple with said operators receiver, and a second transforming means having its primary" in the said busy test circuit and its secondary in a portion of the circuit between said receiver and said line circuit, the flow of current through the secondary of said second transformer being equal and opposite to the flow of current through the secondary of the first mentioned transformer whereby the current flow through said first mentioned transformer will be neutralized with respect to the line with which the operators telephone is connected.

5. In a telephone system, a telephone line, a telephone receiver connected thereto, a busy test circuit, means included in said busy test circuit to render it efi'ective with respect to said telephone receiver but ineffective with respect to said telephone line.

6. In a telephone system, a link circuit, a

I telephone receiver connected thereto, a busy test circuit, and means included in said busy test circuit to render it effective with re- 7 spect to said telephone receiver but inefi'ective with respect to said link circuit.

In witness whereof, I hereunto subscribe my name this 10th day of January A. D., 1916. I

ALBEN E. LUNDELL.

Copies or this patent may be obtainedjor five cents each, by addressing the "Commissioner of Patents, Washington, D. 0." 

